1. Field of the Invention
The present invention relates generally to a coasting mechanism for use in a bicycle, and more particularly to a coasting mechanism which includes a plurality of pawls which substantially simultaneously engage ratchet teeth to transmit a drive force from pedals to a wheel.
2. Description of the Related Art
A bicycle uses a coasting mechanism to alternately link and detach the driving force of the pedals and the rear wheel of the bicycle. Many years ago, the pedals and rear wheel were directly linked, so that the pedals rotated whenever the wheel turned. However, it was found to be desirable to include a mechanism which permits the bicycle to "coast," i.e., to have the wheel turn without turning the pedals. This coasting action has traditionally been accomplished through the use of two pawls which are individually sprung and which permits the pawls to engage ratchet teeth when a driving force is applied, rotating the pawls in one direction with respect to the ratchet teeth, but permit the pawls to pass the ratchet teeth when no driving force is applied and the pawls rotate in the other direction with respect to the ratchet teeth, thereby permitting the wheel to continue rotating without rotating the pedals. Since that time, few changes have been made to this pawl system.
Various other elements have also been connected to a bicycle in similar ways. Some examples of other attachment mechanisms which use a pawl system are found in the patents to Lohman, U.S. Pat. No. 5,004,083; Yang, U.S. Pat. No. 5,083,991; the two patents to Nagano, U.S. Pat. Nos. 5,078,664 and 5,322,487; and Huang et al., U.S. Pat. No. 5,660,083. However, in these patents and the prior art devices, the pawls are individually sprung. This creates a problem, since there are irregularities in the alignment of the pawls and ratchet teeth due to manufacturing limitations, uneven expansion of materials through heat, and a misalignment of parts due to the use of ball bearings in the wheel area, among other things. These irregularities can combine to result in only one pawl engaging the ratchet teeth at a particular time. If only one pawl engages, it will often break, because the load from the driving force is intended to be distributed between two pawls, and thus neither pawl is made strong enough to bear the entire force alone. If one of the pawls breaks, then the other pawl will likewise break once it engages the ratchet teeth, since it alone cannot bear the load.
This problem is accentuated in the area of mountain bike racing. In mountain bike racing, there is a higher force and torque which is applied through the pedals as a driving force than ordinarily encountered in road use. In addition, mountain bike racing is often done on dirt tracks, which increases the probability of dirt or other foreign objects entering the coasting mechanism and interfering with the proper operation of the pawls. In addition, modification of the system to use a single pawl which can withstand the load alone is not appropriate, since this would require too much additional size and weight in the pawl and in the coasting mechanism as a whole, which is not desirable, since increases in size and weight tend to slow a bicycle, rather than provide an edge in racing.
What is needed, therefore, is a coasting mechanism which uses multiple pawls and which includes a linkage which causes the substantially simultaneous engagement of the pawls with the ratchet teeth, to prevent the engagement of one pawl alone. In addition, it is desirable that this coasting mechanism be reduced in size or weight from the standard configuration. It is also desirable that the coasting mechanism be designed to take into account the irregularities which can occur. The present invention includes these and other important features.